An artificial prosthetic device comprised of a stem integrally connected to a neck portion, a head connected to the stem, and two porous tubes disposed about the stem.
Defects of the joints, as a result of hip osteoarthritis, osteoporosis, trauma, occupational overuse, resection of cancerous tissue, and hip joint tumor are among the primary reasons for performing joint replacements. As one example, the hip joint is called a ball-and-socket joint because the spherical head of the thighbone (femur) moves inside the cup-shaped hollow socket (acetabulum) of the pelvis. In a properly functioning hip joint, a series of motions, such as flexion, extension, abduction and adduction, can be carried out to utmost capabilities without stress, strain or pain involved in the motions. After the onset of a hip or hip related diseases and/or fracture, there occurs a wear and tear of the joint and bones and the surrounding ligaments and tendons. This initiates an inflammatory response resulting in pain and swelling of the joint and surrounding tissue, leading to associated diseases and defects. In theses instances, hip replacement surgery is performed to alleviate the symptoms and replace the affected parts.
The use of prosthetic implants is the most successful method used in the cases of limb and joint replacement due to a number of diseases and/or accidents. Implants may be used in hip arthroplasty, total knee replacements, and prosthetic limbs. Hip prosthetics have a success rate of ninety percent for about twenty years, taking into account revision surgery. To duplicate the action of a normal functioning hip joint, a total hip replacement prosthetic implant must have three parts: the stem, which fits into the femur and provides stability; the ball, which replaces the spherical head of the femur and the acetabular cup, which replaces the worn-out hip socket. Each part comes in various sizes in order to accommodate various body sizes and types.
However, even with technological advancements in the design of prosthetic implants, there is still a significant amount of failure, resulting in pain, further damage of region surrounding implant, infection, recurrent arthritic condition and dislocation and the need for revision surgery leading to increase in expenses. U.S. Pat. No. 5,876,446 of Agrawal et al. discloses that xe2x80x9cvirtually all implants currently in use have a tendency to loosen with time, some to the extent of requiring revision.xe2x80x9d According to Agrawal et al., xe2x80x9c. . . the absence of bone in-growth frequently leads to loosening of bone cemented prosthesis.xe2x80x9d
In order to solve this problem, Agrawal et al. provided a metallic press fit prosthetic device comprising at least one porous tissue mating surface on the metallic press fit prosthetic device having interstitial spaces impregnated with a polymer selected from a group consisting of polylactic acid (PLA), polyglutamic acid (PGA), and PLA-PGA copolymers The polymer contains a pharmacologically active substance whose release is controlled over a therapeutically effective period of time. The entire disclosure of U.S. Pat. No. 5,876,446 is hereby incorporated by reference into this specification.
Although the device of Agrawal et al. was an improvement over prior art devices, it still was deficient in certain respects. In the first place, it was not capable of delivering two or more pharmacologically active materials in timed sequence. It also lacked the ability to control the amount of friction produced at the joint and dissipate effectively, the heat produced in other parts of the prosthesis in vivo.
In accordance with this invention, there is provided a prosthetic implant comprised of a stem integrally connected to a neck, a head that sits on top said neck, and porous assembly disposed around the stem. The porous assembly is comprised of a first porous tube and a second porous tube, wherein the second porous tube is disposed within the first porous tube, and wherein the stem is disposed within the second porous tube. The porous assembly is a heat absorbent porous assembly which tends to maintain its temperature within a specified range. The head is comprised of means for releasing a material over a specified period of time.